This patent is a continuation-in-part of U.S. pat. application Ser. No. 870,155, filed June 3, 1986. Now abandoned.
1. Field of the Invention.
The present invention is in the field of hydraulic and earth engineering; more specifically, this invention is in the field of improved wave dissipation and erosion control.
2. Description of the Prior Art.
In the field of erosion control and specifically in the area of protecting or restoring beaches where wave action tends to move sand onto and away from any given area over a period of time, many methods have been utilized in attempts to maintain an existing beach or to restore one which has been washed away. The methods vary in their cost and their effectiveness. For instance, a moderately effective but extremely expensive erosion-control means is the building of a wall or jetty or riprap slightly upstream or in the direction receiving the general wave action. The resulting wave action then breaks on the wall or jetty, which causes turbulence in the wave pattern and causes the flow of water to diminish in the desired beach area. With the interruption of water flow, suspended particulate material, generally sand, drops to the bottom and in a relatively short time forms a beach which is predominantly upstream and, to a lesser extent, downstream from the wall. The beach will be uneven due to the larger quantity of sand buildup on the upstream side of the jetty.
As noted above, the jetty construction is very expensive and requires heavy equipment for the emplacement of the rock. Further, the rock must be massive and hard; sandstone or shale, for instance, would be unsuitable. Therefore, in addition to the heavy equipment, a suitable source of rock must be available within an economic distance.
Where the economics of a source of massive rock do not permit its use, large wire baskets containing smaller rocks have been used. While this method is less costly to install because heavy equipment is not required, the wire tends to corrode and erode with time and the movement of the rock within the basket causes mechanical failure of the basket. Further, flotsam impelled into the basket by storm turbulence can bend and break the baskets. As a result, the rocks become dislodged which leads to a diminution of the effectiveness of this type of erosion control.
In an attempt to meet the problems described above, various methods have been tried. Campbell, in U.S. Pat. No. 3,875,850, describes a massive modular erosion-control device formed of concrete. The design of the module causes an impinging wave to break and drop the suspended sand. Morren, in U.S. Pat. No. 3,953,976, shows a wall formed of modules hingedly affixed at their ends. Rankin, in U.S. Pat. No. 4,297,052, shows a number of units installed and fastened rigidly together, no provision being made for relative movement among the units used. He teaches that under some circumstances, it is necessary to add sandbags to help retain sand and gravel from lake wave action.
In some devices employed for the protection of beach area, the weight of the device, combined with fairly constant low-amplitude motion induced by wave or current, causes the device in effect to burrow, or settle, into the floor beneath the body of water. Over time, the device can practically cease functioning as a wave-disrupting mechanism, requiring replacement of the device or more effort in placing new devices. This severely limits the effectiveness of such devices for protection of a beach.
None of the devices of references cited or the existing art have protected beaches and stopped erosion with the same economy and efficiency as the present invention.